Evaluation of Forced and Self-Excited Vibrations at the Design Stage of Machine-Tool Structures

1986 ◽  
Vol 108 (3) ◽  
pp. 323-329 ◽  
Author(s):  
M. Yoshimura
Keyword(s):  
Machine Tool ◽  
Structural Design ◽  
Design Stage ◽  
Structural Systems ◽  
Damping Properties ◽  
Static Compliance ◽  
Numerical Examples ◽  
Natural Modes ◽  
Modal Flexibility ◽  
Machine Tool Structures

This paper proposes a method for evaluating forced and self-excited vibrations at the design stage of machine-tool structural systems. Cross modal flexibilities between the forced excited and the displacement pick-up points are analyzed. The relationships between the highest allowable values of receptance and vibrational displacement, and the static compliance and modal flexibility are clarified. Then the algorithms of the evaluative methods which use those analyses are given. Using the proposed method, natural modes which must be disregarded in the evaluation of the characteristics can be determined, (1) even when directional orientations of the excited force at points in regard change greatly as a result of states of operations or cannot be definitely determined, and (2) even if damping properties are not clearly known. Designers can judge whether or not a given structural design has vibrational defects. The procedures of the evaluative method are exemplified with numerical examples.

Modelling, Identification and Control of Thermal Deformation of Machine Tool Structures, Part 2: Generalized Transfer Functions

1998 ◽  
Vol 120 (3) ◽  
pp. 632-639 ◽  
Author(s):  
S. Fraser ◽  
M. H. Attia ◽  
M. O. M. Osman
Keyword(s):  
Finite Element ◽  
Machine Tool ◽  
Real Time ◽  
Thermal Deformation ◽  
Transfer Functions ◽  
Design Stage ◽  
Machining Accuracy ◽  
Deformation Problem ◽  
Machine Tool Structure ◽  
Machine Tool Structures

With the ever increasing demand for higher machining accuracy at lower cost, thermal deformation of machine tool structures has to be minimized at the design stage, and compensated for during operation. To compensate for this type of error, two real-time process models are required to identify the magnitude of the transient thermal load and to estimate the relative thermal displacement between the tool and the work piece. Special considerations should be given to the solution of the first ill-posed inverse heat conduction model IHCP. In this paper, the concept of generalized modelling is extended to the thermal deformation problem. The results of this analysis is used to develop expressions for the generalized transfer functions of the thermal, and thermal deformation response of the machine tool structure. These transfer functions are the basic building blocks for real-time solution of the IHCP and then the deformation problem. The latter acts as a feed-back signal to the control system. Finite element simulation of the temperature field and the thermal deformation of a machine tool structure confirmed that the generalized transfer function approach can reproduce the accuracy of the finite element model but two orders of magnitude faster.

Real-Time Adaptive Modeling Approach to Compensate the Thermal Deformation of Nonlinear Machine Tool Structures

2004 ◽  
Author(s):  
S. Fraser ◽  
Helmi Attia ◽  
M. O. M. Osman
Keyword(s):  
Machine Tool ◽  
Temperature Measurement ◽  
Real Time ◽  
Thermal Deformation ◽  
Operating Conditions ◽  
Design Stage ◽  
Frequency Noise ◽  
Adaptive Modeling ◽  
Wide Range ◽  
Machine Tool Structures

Machine tool structures cannot be fully optimized at the design stage to cover the wide range of operating conditions. Therefore, reliable control systems emerge as the logical solution to compensate for thermal errors. Due to the difficulty of measuring the relative thermal displacement δ between the tool and the workpiece during machining, δ has to be accurately estimated in real-time. A new concept of adaptive modeling is introduced to develop control-based dynamic models to predict and compensate for thermal deformation of nonlinear complex machine tool structures. A key element of this approach is to replace the changes in the contact pressures along the joint by fictitious contact heat sources FCHS. This allows us to track the system nonlinearity through temperature measurements and real-time inverse heat conduction IHCP solution. The proposed approach dealt successfully with a number of challenges; namely, the non-uniqueness of the problem, and the lack of sufficient conditions to identify each of such unusual FCHS separately. The results showed that the models are capable of satisfying the accuracy, stability and computational efficiency requirements, even when the temperature measurement signal is contaminated with random noise. The results also showed that the thermal deformation transfer function behaves as low-pass filters, and as such it attenuates the high frequency noise associated with temperature measurement error.

Modelling, Identification and Control of Thermal Deformation of Machine Tool Structures, Part 1: Concept of Generalized Modelling

1998 ◽  
Vol 120 (3) ◽  
pp. 623-631 ◽  
Author(s):  
S. Fraser ◽  
M. H. Attia ◽  
M. O. M. Osman
Keyword(s):  
Machine Tool ◽  
Thermal Deformation ◽  
Infinite Plate ◽  
Measurement Data ◽  
Design Stage ◽  
Machining Accuracy ◽  
Generalized Model ◽  
Real Process ◽  
Machine Tool Structures ◽  
Transient Thermal

With the increasing demand for improved machining accuracy in recent years, the problem of thermal deformation of machine tool structures is becoming more critical than ever. In spite of the effort for improving the thermal deformation characteristics of machine tools at the design stage, there are always some residual errors that have to be compensated for during machining. The design of a generic multi-axis control system requires the development of two models to estimate the transient thermal load and to estimate the thermal deformation of the structure in real-time. To satisfy the stringent accuracy and stability requirements of these two models, a new concept of “generalized modelling” is introduced. It combines mathematical modelling with empirical calibration, and is based on the existence of a mathematical similarity between the real process and a simplified model, referred to as the fundamental generalized problem FGP. To obtain an analytical description of the heat transfer and thermal deformation processes in machine tool structures, an analytical solution of the FGP, which consists of an infinite plate with a central ring heat source, is derived using Hankel transformation. Computer-simulated test cases are presented to demonstrate the use of generalized modelling for predicting the transient thermal response in a complex machine tool structure. It was also shown how the generalized model can accurately extrapolate limited measurement data to predict the entire temperature field. The results confirmed that the generalized model can reproduce the accuracy of the finite-element solution, but two orders of magnitude faster.

Mathematical Model for the Influence of Machine Tool Parts Deformation on Machining Accuracy

2014 ◽  
Vol 556-562 ◽  
pp. 1354-1357
Author(s):  
Li Gong Cui ◽  
Gui Qiang Liang ◽  
Fang Shao
Keyword(s):  
Mathematical Model ◽  
Mathematical Method ◽  
Machine Tool ◽  
Cutting Tool ◽  
Lower Surface ◽  
Design Stage ◽  
Machining Accuracy ◽  
Cutting Point ◽  
The Mathematical Model

This paper presents a mathematical method to analyze the influence of each machine tool part deformation on the machining accuracy. Taking a 3-axis machine tool as an example, this paper divides the machine tool into the cutting tool sub-system and workpiece sub-system. Taking the deformation of lower surface of the machine bed as the research target, the mathematical model of the deformation on the displacement of the cutting point was established. In order to distribute the stiffness of each part, the contribution degree of each part on the machining accuracy was analyzed. Using this mathematical model, the stiffness of each part can be distributed at the design stage of the machine tool, and the machining accuracy of the machine tool can be improved economically.

Exakte posenabhängige Strukurmodelle*/Accurate virtual machine tool structures - Online-identification of the general model of a lightweight machine tool structure with pose-dependent dynamic behavior

2017 ◽  
Vol 107 (05) ◽  
pp. 323-328
Author(s):  
S. Apprich ◽  
F. Wulle ◽  
A. Prof. Pott ◽  
A. Prof. Verl
Keyword(s):  
Machine Tool ◽  
Least Squares ◽  
Dynamic Behavior ◽  
Natural Frequencies ◽  
Recursive Least Squares ◽  
Machine Model ◽  
Online Identification ◽  
Working Space ◽  
Machine Tool Structure ◽  
Machine Tool Structures

Serielle Werkzeugmaschinenstrukturen weisen ein posenabhängiges, dynamisches Verhalten auf, wobei die Eigenfrequenzen um mehrere Hertz im Arbeitsraum variieren können. Die genaue Kenntnis dieses Verhaltens gestattet eine verbesserte Regelung der Strukturen. Ein generelles parametrisches Maschinenmodell, dessen Parameter online durch einen Recursive-Least-Squares-Algorithmus an das reale Maschinenverhalten angepasst werden, stellt Informationen über dieses Maschinenverhalten bereit.   Serial machine tool structures feature a pose-dependent dynamic behavior with natural frequencies varying by serveral hertz within the working space. The accurate knowledge of this behavior allows an improved control of the structures. A general parametric machine model, whose parameters are adapted online to the actual machine tool behavior by a Recursive Least Squares algorithm, provides information about the pose-dependent dynamic behavior.

scholarly journals Comparative Evaluation of Structural Systems for Tapered Tall Buildings

Buildings ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 108
Author(s):  
Kyoung Moon
Keyword(s):  
Structural Design ◽  
Comparative Evaluation ◽  
Building Materials ◽  
Tall Buildings ◽  
Structural Systems ◽  
Lateral Stiffness ◽  
Design Studies ◽  
Structural Efficiency ◽  
Aspect Ratios ◽  
Enormous Amount

Structural efficiency of tapered tall buildings has been well recognized, and many tall buildings of tapered forms have been built throughout the world. Tall buildings are built with an enormous amount of building materials. As one of the most efficient structural forms for tall buildings, the contribution of tapered forms to saving structural materials coming from our limited natural resources could be significant. Structural design of tall buildings is generally governed by lateral stiffness rather than strength. This paper systematically studies the structural efficiency of tapered tall buildings in terms of lateral stiffness. Tall buildings of various heights and angles of taper are designed with different structural systems prevalently used for today’s tall buildings, such as diagrids, braced tubes, and core-outrigger systems. The heights of the studied buildings range from 60 to 100 stories, and the corresponding height-to-width aspect ratios in their non-tapered prismatic forms range from 6.5 to 10.8. The angles of taper studied are 1, 2, and 3 degrees. Gross floor area of each building of the same story height is maintained to be the same regardless of the different angles of taper. Based on design studies, comparative evaluation of the various structural systems for tapered tall buildings is presented.

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